In general when food is ingested into the stomach, initially, the elastic upper portion or fundus accommodates the food and the fundus expands. As food enters and the fundus expands there is a pressure gradient created in the stomach between the fundus and the antrum (fundus pylori). A number of things occur at this time. Fluids tend to be pushed through the pylorus, which acts as a leaky valve. Peristaltic contractions move down the stomach from the fundus into the antrum to mix and break down food and propel small particles through the pylorus into the duodenum. In healthy human stomachs, peristalsis is believed to be controlled at least in part by a region of the stomach identified near the interface of the fundus and the corpus along the greater curvature. In this region, there are cells believed to govern the organs' periodic contractile behavior that generate and propagate rhythmic electrical signals that correspond to the contractile behavior of the stomach. These characteristic contractions are believed to create, a pressure gradient between the fundus pylori (or antrum) and duodenum that relates to the rate of gastric emptying. When the contractions begin, the pylorus is generally closed, although fluid and small particles leak through the valve. As contractions or electrical activity corresponding to the contractions reach pylorus, the pylorus begins to open or relax. Thus, as the stomach churns and breaks down food in a healthy stomach, the pylorus begins to open. As this is occurring, there may be electrical activity in the duodenum as well. Retrograde electrical activity from the duodenum, i.e. contractions or electrical activity in the direction of the pylorus tends to cause the pylorus to close, thus preventing bile and pancreatic juices from backing up into the stomach. Accordingly, the opening and closing of the pylorus is influenced by electrical stimulation input from both of its ends.
In a number of disease states or conditions, the contractions of the stomach and/or the opening and closing of the pylorus is irregular. Gastroparesis may result from insufficient contractions to churn food, move food through the pylorus, and/or open the pylorus, among other things, resulting in gastro-retention of food. In another motility disorder known as dumping syndrome, the stomach empties at an abnormally high rate into the small intestine causing various gastrointestinal disorders. It has also been observed that in obese patients, gastric emptying tends to be at a higher than normal rate. It is believed that obesity may be treated by altering gastric motility to cause the stomach to slow gastric emptying.
Accordingly, it would be desirable to provide a device and method for controlling gastric emptying. Further, it would be desirable to provide a device and method that controls the contracting and relaxation of the pylorus according to a desired increase or decrease in gastric emptying.
Some devices have been proposed to constrict the stomach to reduce stomach volume. These devices are typically implanted in a relatively invasive procedure and operate to constrict the stomach but do not enable periodic control of the stomach emptying. Some devices have been proposed to interfere with the peristaltic motion of the gastrointestinal tract and especially the stomach, to slow the movement of food from the stomach. These devices control the contractions of the stomach but are not directed to opening and closing the pylorus outside of the context of controlling peristalsis of the stomach. Furthermore, most of these devices require open or laparoscopic surgery in which a stimulator unit is implanted subcutaneously adjacent the abdomen wall with leads extending to the stomach where electrodes are attached. Artificial sphincters, for opening and closing sphincters including the pylorus have been proposed. These devices typically involve placing a constricting member around the sphincters in a relatively invasive procedure.
Accordingly it would be desirable to provide a relatively easily implanted device and method for controlling the opening and/or closing of the pylorus. It would further be desirable to provide a method and device for treating obesity.